Refrigeration apparatus and method of operating for powered and nonpowered cooling modes

ABSTRACT

This specification discloses the method and apparatus for operating a refrigeration system in both powered and nonpowered (free cooling) modes of operation including the method and apparatus for rapidly converting from one mode to the other.

O Umted States Patent 1 [111 3,744,273

Ware [451 July 10, 1973 [54] REFRIGERATION APPARATUS AND 2,836,966 6/1958 Koctiller 62/174 METHOD OF OPERATING FOR POWERED 2,952,137 9/1960 Wa ns 62/174 AND NONPOWERED COOLING MODES 3,214,932 11/1965 Grant 62/174 3,242,689 3/1966 Chubb 62/498 [75] Inventor: Chester I), Ware, La Cr e, Wis 3,315,484 4/1967 Ross 62/174 [73] Assignee: The Trane Company, La Crosse,

i Primary ExammerW1l1iam vJ. Wye

Attorney-Arthur 0. Andersen et al.

[22] Filed: Mar. 27, 1972 [21] Appl. No.: 238,410 [57] ABSTRACT [52] US. Cl 62/498, 62/149, 621174 This specification discloses the method and apparatus 62/510, 62/512, 62/l96, 62/1 15, 62/117 for operating a refrigeration system in both powered [51] Int. Cl. F25b 1/00 and nonpowered (free g) modes of p at n- [58] Field of Search 62/149, 174, 5 l2, cluding h me h nd apparatus for rapidly convert- 62/1 15, 117, 498 196 ing from one mode to the other.

[56] References Cited UNITED STATES PATENTS 5 Claims, 3 Drawing Figures 2,225,491 12/1940 Voorhees 62/512 OCGOOOOOOO oooooooooo OOOOOOOOO PATENTEDmumsn 3.744.273

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REFRIGERATION APPARATUS AND METHOD OF OPERATING FOR POWERED AND NONPOWERED COOLING MODES BACKGROUND OF THE INVENTION During certain seasons when the cooling load is relatively small such as less than 40 percent peak load and if the heat sink is sufficiently cool, it is possible to operate compressor type refrigeration systems, such' as for cooling a building, without energizing the compressor. Refrigerant vapor is simply conveyed without compression to a condenser which is maintained at a lower temperature than the evaporator. The condensed refrigerant flows back to the evaporator to again be reevaporated by the heat from the building conveyed thereto such as by the building chilled water system. The mode of operation is conducted without operation of the compressor, hence its name free cooling.

In order that the free cooling mode can be operated with a high degree of capacity, it has been found necessary to provide a bypass around the compressor to permit vapor from the evaporator to pass without much restriction to the condenser and to provide a bypass around liquid flow control device to permit free flow of liquid from the condenser to the evaporator. Further it has been found necessary to provide special means of more fully wetting the tubes in the evaporator with refrigerant to increase the evaporator capacity. This is so because refrigeration systems are ordinarily charged with a minimum of refrigerant sufficient only to wet all of the evaporator tubes-during full load conditions. Because of the violent boiling of the refrigerant under these conditions and the presence of flash gas entering the evaporator, the equivalent quiescent refrigerant level is ordinarily maintained substantially below the top of the tube bundle in the evaporator. For purposes of this disclosure equivalent quiescent level is intended to mean the level of refrigerant in the evaporator if suddenly all boiling were to cease without any further ingress or egress of refrigerant to or from the evaporator.

Thus when first attempts were made to operate ordinary refrigeration systems in a free cooling mode, it was found that the evaporator capacity was excessively low due to the lack of refrigerant liquid on the middle and upper rows of tubes.

Several schemes to remedy this problem have been suggested. One scheme that utilizes a refrigerant liquid pump to spray refrigerant liquid over the evaporator tubes is described in US. Pat. No. 2,718,766.

Another scheme adds refrigerant for the free cooling mode to immerse all of the tubes of the evaporator and is illustrated in US. Pat. No. 3,l91,396. In this latter patent a special chamber is provided for storing the additional refrigerant. This chamber is located below the upper most tubes of the evaporator and is filled with refrigerant liquid from the evaporator by venting the special chamber with the evaporator until substantially a common level is reached in the evaporator and special chamber. Only after this level is reached are the chamber liquid line and vent valves closed and the compressor allowed to start for a powered mode of operation. Thus considerable time may be consumed to pass from a free cooling mode to a powered mode of operation.

Likewise considerable time may be consumed to prepare the system for free cooling. A small heater is provided in the special chamber to heat the refrigerant. Only after the refrigerant has reached a certain pressure, would refrigerant be forced to higher levels in the evaporator.

SUMMARY OF THE INVENTION This invention is distinct from the aforementioned prior art as it does not utilize the time consuming means of pressurizing the refrigerant to obtain transfer of the added refrigerant to the evaporator. Furthermore means are provided for resuming normal operation of the compressor immediately upon switching from a free cooling mode of operation to the powered mode of operation.

The first of these distinctive features is accomplished by allowing a predetermined additional liquid refrigerant to flow by gravity to the evaporator without the necessity of pressurizing any liquid refrigerant.

The second mentioned of these distinctive features is accomplished by utilizing the compressor under power to transfer refrigerant from the evaporator to an area where it may be retained out of the evaporator zone.

This invention thus provides a method of operating a refrigeration system which may be converted from a free cooling mode to a powered mode of operation and vice versa without undue delay between the modes of operation.

More specifically this invention provides refrigeration apparatus adapted to be operated in the cooling mode alternatively with the compressor operating and without the compressor operating comprising: a refrigerant evaporator, a refrigerant compressor, and a refrigerant condenser disposed above said evaporator serially connected in a closed refrigerant circuit; a liquid refrigerant storage chamber outside said refrigerant circuit disposed above said evaporator and below said condenser for storing liquid refrigerant during operation of said compressor; first conduit means connecting the lower portion of said condenser with said storage chamber for conducting via force of gravity liquid refrigerant from said condenser to said storage chamber; second conduit means for connecting said storage chamber to said evaporator for conducting via force of gravity refrigerant liquid from said storage chamber to said evaporator; first valve means in said second conduit means for terminating flow from said storage chamber during operation of said compressor; third conduit means connecting said evaporator to said condenser; and second valve means in said third conduit means for terminating flow of refrigerant vapor through said third conduit means during operation of said compressor.

Other aspects and advantages will be apparent as the specification proceeds to describe the invention in detail with reference to the drawings in which like reference characters are used to designate like elements throughout wherein:

FIG. 1 is a semi-schematic of a refrigeration machine constructed in accordance with this invention,

FIG. 2 is a simplified schematic electric diagram for the machine shown in FIG. 1, and

FIG. 3 is a modification of the schematic of FIG. 2 whereby the operating modes may be made completely automatic.

Now with reference to the refrigeration machine shown in FIG. 1 it will be seen that the refrigeration systern 10 includes a refrigerant evaporator 12, a refriger- 3 ant compressor 14, and a refrigerant condenser 16. The evaporator 12 is of the flooded shell-and-tube type having a bundle of horizontal tubes 18 through the interior of which water warmed by a load, such as a building, is conducted via inlet and outlet headers (not shown) to boil refrigerant within the evaporator shell. The refrigerant vapor is conducted to the compressor 14 via an inlet conduit 24. The compressor 14 shown is intended to designate a two stage compressor although aspects of the instant invention are equally applicable to single stage compressor refrigeration systems. The inlet of the first stage is provided with inlet vanes for controllably throttling the flow of refrigerant to the compressor. It is common practice to control such inlet vanes in response to the temperature of water leaving the evaporator for the building.

As the water temperature rises, the vanes are opened to thereby load the compressor. Such inlet vanes 26 have been placed in the inlet conduit 24 for purposes of illustration, it being understood that such vanes are generally located with the confines of the compressor shell per se. The compressor input shaft is connected to a drive motor which may be an electric motor, steam turbine or other form of prime mover 28. if electric, motor 28 could also may be confined within the compressor shell to thereby make the compressor hermetic.

The vapor discharged from the compressor is conducted via compressor outlet conduit 30 to the condenser 16 which may be also of the shell-and-tube type wherein cooling water such as from a cooling tower is passed through the tubes via cooling water inlet and outlet header connections (not shown).

Refrigerant condensed at the outer surface of the tubes flows during the powered mode of operation from the condenser shell downwardly through a stand pipe 36 through a first flow control device 38 which may take the form of a fixed orifice flow control valve, such as 38 described in US. Pat. No. 3,260,067 assigned to the assignee of this invention, or the form of a more conventional variable orifice float valve.

The refrigerant then passes from the valve 38 through a conduit 40 to an economizer flash chamber 42. The flash gas from the economizer 42 is conducted via conduit 44 to inlet of the second stage of compressor 14 for recompression. The liquid refrigerant from the economizer is conducted to a second stand pipe 46 which leads to a second flow control device 48, which may be similar to flow control device 38, from whence the refrigerant is conducted via conduit 50 to be distributed into the evaporator shell. The operation and advantages of an economizer are well known and for the sake of brevity will not be further discussed here.

For purposes of carrying out the preferred embodiment of the instant invention, a chamber 52 is located below condenser 16 and above evaporator 12. Chamber 52 is used as a means for storing a predetermined additional amount of liquid refrigerant and thus preventing this additional quantity of refrigerant from returning to the evaporator when the system is operated in the powered mode. A conduit 56 connects the bottom of condenser 16 to the top of chamber 52. The inlet of conduit 56 is slightly lower than the inlet of stand pipe 36 so refrigerant condensate preferentially enters chamber 52 until chamber 52 has been filled.

For purposes of carrying out the free cooling mode of operation in accordance with the methods of this invention, the bottom of chamber 52 is connected via conduit 57 having an automatically powered normally closed shut off valve 62 to conduit 50. Furthermore there is provided a compressor vapor bypass conduit 66 extending between upper portions of the shells of condenser 16 and evaporator 12.

Conduit 66 is also provided with an automatically powered normally closed shutoff valve 64.

The method of operating the above described refrigeration system may best be understood by referring further to the schematic diagram of FIG. 2. For purposes of this description let it be assumed that the system had previously been operating with power and that chamber 52 accordingly is substantially full of liquid refrigerant and that the equivalent quiescent level of liquid refrigerant in the evaporator is correspondingly reduced by the predetermined quantity of refrigerant retained in chamber 52. Further let it be assumed that conditions are such that the free cooling mode of operation is preferred, i.e. the load is less than about 40 percent of full load and that the temperature of condenser cooling water is sufficiently below the desired temperature for the water leaving evaporator 12.

The system is set into the free cooling mode of operation simply by moving switch 68 into the solid line position to complete a circuit from line 1 to line 2 including switch 68, the actuator of valve 62 and the actuator of valve 64 whereby valves 62 and 64 are powered to the fully open positions. A second circuit is also completed which includes switch 68, normally closed contact 69, and actuator control 72 for inlet vanes 26.

The opening of valve 62 permits substantially all of the liquid refrigerant retained in chamber 52 to be immediately dumped into the evaporator 12 thereby raising the liquid refrigerant therein to a high level 78 to immerse substantially all the tubes of the evaporator. The opening of valve 64 permits refrigerant vapor to pass freely from evaporator 12 to condenser 16 whereupon it is condensed and returned via conduit 56, chamber 52, conduit 57, valve 62 and conduit 50 to evaporator 12. A secondary path for passage of refrigerant vapor from condenser 12 to evaporator 16 also is provided by conduit 24, compressor 14 and conduit 30. It should be reiterated that during this mode of operation compressor 14 is not operated, however the compressor does not block the free flow of refrigerant therethrough. Upon the aforementioned energization of actuator 72, vanes 26 are actuated from a preset minimum opening to the fully open position.

Should the load exceed the capacity of the system as operated on the free cooling mode, switch 68 may be instantaneously placed in the dot-dash line position of FIG. 2 whereby valves 62, 64 are immediately closed and vanes 26 returned to a minimum opening position. Furthermore a first circuit is immediately energized including switch 68, and contactor coil 80 whereupon contacts 82 are immediately closed to energize a second circuit including switch 68, contacts 82 and compressor motor 28. A third circuit is established including switch 68, rheostat 84, contacts 35, and vane actuator 72 whereby vanes 26 are immediately moved to a second preselected minimum position at which excessive quantities of liquid refrigerant will not be drawn into the compressor inlet despite the high level of refrigerant in the evaporator. This minimum may be manually adjusted at rheostat 84. A fourth circuit is also established including switch'68 and coil 86 of snap-acting time delay relay 88.

Time delay relay 88 includes contacts 69 and 85 (previously mentioned) and contacts 90. The relay has two positions; a first position in which contacts 69 and 85 are closed and contacts 90 open; and a second position in which contacts 69 and 85 are open and contacts 90 closed. The relay is intended to be snap-acting, i.e. movement from one position to the other position is substantially instantaneous. However, the movement from the first position to the second position is not effected immediately upon energization of coil 86 as this movement is delayed for a predetermined time by action of single way dash-pot 92. The time delay selected is the time that it takes to insure that the level of refrigerant in the evaporator has fallen to that at which no danger of excessive liquid refrigerant carryover into the compressor will take place. After this period of time contacts 85 are opened and contacts 90 closed thereby placing the control of the vanes upon bellows actuator 74 whose sensor bulb 76 is located at the evaporator water outlet responsive to the load. It should be appreciated that both coils 86 and 80 are selected to have sufficiently high impedance whereby they have no substantial effect upon other parallel circuits.

Now considering the system operation upon moving switch 68 from the free cooling mode to the powered mode, the following events happen. Valves 62 and 64 are immediately closed. The compressor is immediately started. The vanes 26 immediately and temporarily assume a minimum open position whereby refrigerant gas is withdrawn from the evaporator, compressed and delivered to the condenser. The rate is limited to prevent liquid carryover. The condensed refrigerant preferentially passes via gravity through conduit 56 into chamber 52. When chamber 52 has been filled, liquid refrigerant passes down stand pipe 36 through flow control 38 into flash chamber 42, the gaseous portion being returned to the second stage of the compressor and the liquid portion being delivered to the evaporator via conduit 46 and flow control 48 for re-evaporation.

Because this quantity of refrigerant in chamber 52 and conduits 56 and 57 is not permitted to return to the evaporator during the powered mode, the equivalent quiescent refrigerant level in the evaporator is reduced to a lower level designated at 94. After sufficient time has lapsed by action of dash-pot 92 to insure that the lower level has been reached so that no excessive liquid carryover to the compressor will take place, relay 88 is switched thereby placing vanes 26 at the control of load sensor 76. If at any time during the powered mode it is desired to switch to the free cooling mode, it is only necessary to place switch 68 in the solid line position and the free cooling mode aforedescribed will be resumed.

Thus it will be seen that the method of operation permits the refrigeration system to be switched from the frcc cooling mode to the powered mode or vice versa with only a single movement of switch 68. The reduction of evaporator refrigerant level is extremely fast as this is done with the assistance of the energized compressor. The filling of chamber 52 with liquid refrigerant requires only gravity and is not dependent upon pressure differentials in the system. The returning of the additional refrigerant to the evaporator upon switching to the free cooling mode is also extremely fast as the additional refrigerant is literally dumped into the evaporator upon opening of valve 62.

Because of this extremely rapid response, it is possible to completely automate the operative modes simply by automating switch 68. Thus in the modification shown in FIG. 3 switch 68a is an automatic version of switch 68 and is moved to the power mode position (dash-dot line) by energization of solenoid actuator 95 and to the free cooling position (solid line) by deenergization of actuator 95. Solenoid 95 is disposed in series with parallel switch 96 and 98. Switch 96 is actuated by a bellows and bulb sensor to close at a predetermined high temperature and is arranged to sense condenser inlet water temperature. Switch 98 is actuated by a bellows and bulb sensor to close at a predetermined high temperature and is arranged to sense evaporator outlet water temperature. Thus if either the condenser temperature is too high for free cooling as indicated by closure of switch 96 or the refrigeration load too great for free cooling as indicated by closure of switch 98, switch 68a will be positioned for the power mode. Only when the condenser water is sufficiently cool and the refrigeration load suffieiently light to permit free cooling will switch 68a be placed in the free cooling position.

It should be appreciated that the controls shown have been greatly simplified to clearly illustrate the invention. Obviously many variations can be made both to these controls and the apparatus without departing from the true spirit of the invention. I accordingly 'desire my invention to be limited only by the claims.

I claim:

1. Compression refrigeration apparatus adapted to be operated in the cooling mode alternatively with the compressor operating and without the compressor operating comprising: a refrigerant evaporator, a refrigerant compressor, and a refrigerant condenser disposed above said evaporator seriallyconnected in a closed refrigerant circuit; a liquid refrigerant storage chamber outside said refrigerant circuit disposed above said evaporator and below said condenser for storing liquid refrigerantduring operation of said compressor; first conduit means connecting the lower portion of said condenser with said storage chamber for conducting via force of gravity liquid refrigerant from said condenser to said storage chamber; second conduit means for connecting said storage chamber to said evaporator for conducting via force of gravity refrigerant liquid from said storage chamber to said evaporator; first valve means in said second conduit means for terminating flow from said storage chamber during operation of said compressor; third conduit means connecting said evaporator to said condenser; and second valve means in said third conduit means for terminating flow of refrigerant vapor through said third conduit means during operation of said compressor.

2. The apparatus as defined by claim 1 including an economizer in said closed refrigerant circuit between said condenser and evaporator for receiving refrigerant from-said condenser and means for preferentially directing refrigerant condensate from said condenser to said first conduit means.

3. The apparatus as defined by claim 1 including means for preferentially directing refrigerant condensate from said condenser to said first conduit means.

4. The apparatus as defined by claim 1 wherein said first conduit means functions to simultaneously supply liquid refrigerant to said storage chamber from said chamber to said condenser thereby permitting passage of refrigerant gas from said storage chamber to said condenser upon filling said storage chamber with refrigerant liquid. 

1. Compression refrigeration apparatus adapted to be operated in the cooling mode alternatively with the compressor operating and without the compressor operating comprising: a refrigerant evaporator, a refrigerant compressor, and a refrigerant condenser disposed above said evaporator serially connected in a closed refrigerant circuit; a liquid refrigerant storage chamber outside said refrigeraNt circuit disposed above said evaporator and below said condenser for storing liquid refrigerant during operation of said compressor; first conduit means connecting the lower portion of said condenser with said storage chamber for conducting via force of gravity liquid refrigerant from said condenser to said storage chamber; second conduit means for connecting said storage chamber to said evaporator for conducting via force of gravity refrigerant liquid from said storage chamber to said evaporator; first valve means in said second conduit means for terminating flow from said storage chamber during operation of said compressor; third conduit means connecting said evaporator to said condenser; and second valve means in said third conduit means for terminating flow of refrigerant vapor through said third conduit means during operation of said compressor.
 2. The apparatus as defined by claim 1 including an economizer in said closed refrigerant circuit between said condenser and evaporator for receiving refrigerant from said condenser and means for preferentially directing refrigerant condensate from said condenser to said first conduit means.
 3. The apparatus as defined by claim 1 including means for preferentially directing refrigerant condensate from said condenser to said first conduit means.
 4. The apparatus as defined by claim 1 wherein said first conduit means functions to simultaneously supply liquid refrigerant to said storage chamber from said condenser and to vent refrigerant vapor from said storage chamber to said condenser.
 5. The apparatus as defined by claim 4 wherein said first conduit means defines a single passage way inclined upwardly from the upper portion of said storage chamber to said condenser thereby permitting passage of refrigerant gas from said storage chamber to said condenser upon filling said storage chamber with refrigerant liquid. 